Sealing arrangement

ABSTRACT

A sealing assembly comprises a bore in a housing, a plurality of seal rings and a shaft. The bore comprises a plurality of seats disposed at different seat radius for the seal rings. The bore comprises for each pair of adjacent seats axially inward of an inner end of the outward seat and proximate to the inward seat a chamfer extending radially inwardly over an inward axial distance. The chamfer between each pair of seats allows for the radial contraction of the seal rings upon assembly.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to EP Application07405017.0 filed in Europe on Jan. 19, 2007, and as a continuationapplication under 35 U.S.C. §120 to PCT/EP2008/050359 filed as anInternational Application on Jan. 15, 2008 designating the U.S., theentire contents of which are hereby incorporated by reference in theirentireties.

TECHNICAL FIELD

Subject matter disclosed herein relates generally to the technical fieldof turbomachinery for internal combustion engines and, in particular,seals for rotating turbomachinery shafts.

BACKGROUND INFORMATION

Most turbines include a shaft that extends from a hub of a turbine wheelto a shaft bearing. For example, turbines of exhaust gas turbochargersfor internal combustion engines typically include a turbine wheelhousing that directs exhaust of an engine to a turbine wheel and anotherhousing that houses a bearing for a shaft coupled to the turbine wheel.In such an arrangement, the bearing exists in a lubricant environmentthat lubricates the bearing to reduce frictional forces, dampenvibration, etc., to thereby allow for high speed operation of theturbine, and the turbine wheel exists in an exhaust environmenttypically characterized by high temperatures, high pressures and,depending on nature of the exhaust, corrosive reaction chemistry. Toseparate these two environments, a variety of seal mechanisms have beenproposed and used.

In general, such seal mechanisms aim to reduce flow of exhaust to thelubricant environment and/or flow of lubricant to the exhaustenvironment, both of which can be detrimental to performance (e.g.,efficiency, emissions, longevity, etc.). Flow of exhaust to thelubricant environment is usually referred to as “blowby” and flow oflubricant to the exhaust environment is usually referred to as“leakage”. Blowby typically occurs during high speed operation or loadwhere a significant positive pressure differential exists between theexhaust environment and the lubricant environment.

Leakage typically occurs during low turbine-power modes of operation,such as at engine idle, where the pressure differential is negativeand/or minimal and insufficient to overcome capillary or other lubricanttransport forces.

As the turbomachinery industry trends toward increased turbine inletpressures, more stringent emission regulations, closed-crankcaseventilation systems, and increased customer sensitivity to the passageof exhaust gas through the turbine seal, a need for seal mechanisms thatreduce blowby and/or leakage will increase, and the design of suchmechanisms will become more challenging. Various exemplary sealingassemblies disclosed herein aim to reduce blowby and/or leakage.Further, various exemplary sealing assemblies may allow for increasedperformance (e.g., efficiency, emissions, longevity, etc.), assemblyand/or disassembly of turbomachinery.

US 2006/0002803 A1, which is hereby incorporated by reference herein,discloses an exemplary bore for a shaft of a turbomachine including aplurality of seal rings. An exemplary sealing assembly includes two sealrings, a radial inner surface of the bore and an outer surface of theshaft that act together to create resistance to flow. The seal mechanismcreates resistance via a tortuous path and reduced flow area, sometimesreferred to as a labyrinth seal. The surface of the turbine bore segmentincludes an outer seat. The inner surface of the turbine bore segmentalso includes an inner seat. The outer seat receives the outer ringwhile the inner seat receives the inner ring. The exemplary shaftincludes an outer slot that substantially coincides with the outer ringand an inner slot that substantially coincides with the inner ring. Theaxial width of the recess of the outer seat, is selected to be smallerthan the axial width of the inner ring. This allows the inner ring tobridge and axially traverse the outer seat upon installation of theinner ring. Further embodiments of the exemplary bore for a shaft of aturbomachine as well as an exemplary method for positioning a pluralityof seal rings on a shaft is disclosed in US 2006/0236694 A1, which ishereby incorporated by reference herein, and in US 2006/0236695 A1,which is hereby incorporated by reference herein.

SUMMARY

A sealing assembly for a shaft of a turbomachine in a bore of a housingis disclosed.

A sealing assembly for sealing a shaft of a turbomachine in a bore of ahousing, said shaft extending from a hub of a turbine wheel to a shaftbearing in said housing, the assembly comprising at least two seal ringsand the bore comprising: longitudinal axis extending generally from aninner end to an outer end of the bore, said outer end of the bore beingadjacent said hub of the turbine wheel; an outer seat disposed proximateto the outer end of the bore at an outer seat radius for an outer sealring, and an inner seat disposed axially between the outer seat and theinner end of the bore at an inner seat radius for an inner seal ring,wherein the bore comprises axially inward of an inner end of the outerseat and proximate to the inner seat a chamfer extending radiallyinwardly over an inward axial distance to an inner chamfer plateauradius.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the disclosure may be had by referenceto the following detailed description when taken in conjunction with theaccompanying drawings wherein:

FIG. 1 is a cross-sectional view of an exemplary housing of aturbocharger,

FIG. 2 is a cross-section view of an exemplary sealing assembly for abore and a shaft,

FIG. 3 is a close-up of the exemplary sealing assembly of FIG. 2,

FIG. 4 is a close-up of the bore of the exemplary sealing assembly ofFIG. 2,

FIG. 5 is a side view of a section of the step gap seal ring with thestop element before the mounting, and

FIG. 6 is a side view of a section of the contracted step gap seal ringof FIG. 5 after the mounting.

DETAILED DESCRIPTION

The inventive sealing assembly comprises a bore in a housing, aplurality of seal rings and a shaft operably coupled to a turbine wheelwherein the bore, the seal rings and the shaft form a labyrinth seal.The bore comprises a plurality of seats disposed between an inner and anouter end of the bore at different seat radius for the seal rings. Ofeach pair of adjacent seats, the seat radius of the outward seat exceedsthe seat radius of the inward seat. The bore comprises for each pair ofadjacent seats axially inward of an inner end of the outward seat andproximate to the inward seat a chamfer extending radially inwardly overan inward axial distance. The chamfer between each pair of seats allowsfor the radial contraction of the seal rings upon assembly.

In order to reduce leakage, an inwardly facing annular groove isoptionally disposed between the innermost seal ring and the other sealrings. The annular groove leads into a drain channel located at thebottom of the annular groove. The drain channel is connected to thelubricant environment. The cross section of the drain channel can bebigger than the minimal cross section formed by the gap between theinnermost seal ring and the shaft.

For the assembly of the seal ring in the shaft, the seal rings areoptionally divided by a split. As this split affects the flow areathrough and around the seal rings, it is desirable to maintain thissplit at a minimum typically dictated by necessity to allow forinstallation and/or thermal expansion during operation. To compensatefor any detrimental effect such an example may have on seal performance,a step gap geometry may be employed in the seal rings to increase flowresistance. In order to limit the radial extension of the seal ringbefore the assembly, the split can have a stopper configuration, or stopelement. As the stop element limits the radial extension of the sealring, the size of each chamfer can be minimised.

Turbochargers are typically utilized to increase the output of aninternal combustion engine. The internal combustion engine includes anengine block housing one or more combustion chambers that operativelydrive a shaft. An intake port provides a flow path for air to the engineblock while an exhaust port provides a flow path for exhaust from theengine block. The turbocharger acts to extract energy from the exhaustand to provide energy to intake air, which may be combined with fuel toform combustion gas. The turbocharger typically includes an air inlet, ashaft, a compressor, a turbine, a bearing housing and an exhaust outlet.

FIG. 1 shows a cross-section of an exemplary housing 20 for housing abearing to support a turbine wheel shaft. The exemplary housing 20includes a through bore 25. In general, such a through bore has alongitudinal axis A that is coaxial with the axis of rotation of aturbine wheel and a compressor wheel. A dashed box indicates anexemplary sealing assembly of the turbine bore segment of the bore 25that is shown in more detail in FIGS. 2, 3 and 4 along with additionalcomponents.

FIG. 2 shows a cross-section of the exemplary sealing assembly of theturbine bore segment along with seal rings 31, 32 and 33 and a shaft 10.Shaft 10 comprises a section that includes a plurality of radiallyoutwardly opened annular slots, which are capable of receiving said sealrings. In general, the radially outwardly opened slots are cut in theturbine shaft sufficiently inboard of the joint between the shaft andthe turbine wheel to avoid a heat affected zone. Optionally, the sectionof the shaft comprising the radially outwardly opened slots may beformed by a separate, ring shaped bush 15.

The close-up of the exemplary sealing assembly in FIG. 3 shows aplurality of seats included in the inner surface of bore 25. There is acorresponding seat to each radially outwardly opened slot. An outerradially outwardly opened slot 11 receives the outer seal ring 31 whichis seated in an outer seat 21 of the bore. An intermediate radiallyoutwardly opened slot 12 receives the intermediate seal ring 32 which isseated in an intermediate seat 22 of the bore. Finally, an innerradially outwardly opened slot 13 receives the inner seal ring 33 whichis seated in an inner seat 23 of the bore. To allow for installation,the axial width of a radially outwardly opened slot slightly exceeds theaxial width of a respective seal ring.

Each of the seats included in the inner surface of bore 25 has aradially inwardly extending step on its inward side. As shown in detailin FIG. 4, an outer step 212 of outer seat 21 extends radially inwardlyto an outer step radius s₂₁, which is smaller than outer seat radius r₂₁of outer seat 21. An intermediate step 222 of intermediate seat 22extends radially inwardly to an intermediate step radius s₂₂, which issmaller than intermediate seat radius r₂₂ of intermediate seat 22. Aninner step 232 of inner seat 23 finally extends radially inwardly to aninner step radius s₂₃, which is smaller than inner seat radius r₂₃ ofinner seat 23. These steps of the seats generally limit inward movementof the rings. The seats optionally include a small, radially inwardlyopen groove adjacent the step.

During use or operation, a seal ring will typically wear-in under gasloading until an edge of the seal ring contacts the radially inwardextending step in its seat wherein such contact can serve to limitfurther wear of a ring.

The seal rings 31, 32 and 33, the radially inward surface of the turbinebore segment 25, and a radially outward surface of the shaft 10 acttogether to create resistance to flow of exhaust to the lubricantenvironment (blowby). The seal mechanism creates resistance via atortuous path and reduced flow area, sometimes referred to as alabyrinth seal. The outer seal ring 31, the intermediate seal ring 32and the inner seal ring 33 act to create resistances in series.

The exemplary sealing assembly includes features that facilitateassembly and/or disassembly of the shaft 10 from the bore 25. Aparticular feature that facilitates assembly and/or disassembly is thevarious chamfers in the wall of the bore. Outside of the outer end ofthe outer seat 21, there is a chamfer 211 extending radially outwardover an outward axial distance from an outer chamfer plateau radius p₂₁.Between each pair of seats in the bore, there is a chamfer extendingradially inwardly over an inward axial distance. Between the outer seat31 and the intermediate seat 32, there is a chamfer 221 extendingradially inward over an inward axial distance to an intermediate chamferplateau radius p₂₂. Between the intermediate seat 32 and the inner seat33, there is a chamfer 231 extending radially inward over an inwardaxial distance to an inner chamfer plateau radius p₂₃.

The chamfers extend radially inward over a radial distance. Thisdistance is at least slightly exceeding the difference between the outerradius of the seal ring before the mounting and the radius of thecorresponding seat. In other words, the widest radius of each chamfer isexceeding the outer radius of the corresponding seal ring before themounting, as indicated in FIG. 4 by the non-compressed seal rings 31, 32and 33 at the right side of the drawing. In order to further facilitatemounting of the seal rings, the widest radius of each chamfer can beenlarged thus further extending the distance the chamfers extendradially inward. Also, the corresponding radially outwardly opened slotin the shaft has to be radially deep enough to allow the seal ring tocontract radially during the mounting.

The inner end of the inner seat 23 has a step 232 limiting movement ofthe corresponding seal ring in axial inward direction. In addition, atthe outer end of the inner seat there is optionally a chamfer 233extending radially inwardly over an outward axial distance to the innerchamfer plateau radius p₂₃. The distance from the step 232 of the innerseat 23 to the chamfer 233 is optionally selected to allow for adequateexcursion of the inner ring 33 in the inner seat 23 during use oroperation. Should the inner ring 33 reach the chamfer 233 during use oroperation, the chamfer will offer some resistance to further axialoutward movement of the inner ring 33 toward the turbine end of thebore, which may vary depending on chamfer rise angle, chamfer risedistance, chamfer cross-section, etc.; however, such resistance maytypically be overcome during assembly and/or disassembly.

In order to further improve the sealing performance regarding theleakage of lubricant, an inwardly facing annular groove 26 is optionallydisposed between the inner seat and the other seats. The annular grooveis connected to the lubricant environment by a drain channel 27 locatedat the bottom of the annular groove. Lubricant passing the inner seal isbeing collected in the annular groove and lead back to the lubricantenvironment through the drain channel.

The cross section of the channel can be bigger than the minimal crosssection formed by the gap between the inner seal ring and the shaft toallow for sufficient lubricant drainage.

While the exemplary chamfers shown have substantially linearcross-section, other examples may include chamfers with non-linearcross-section, optionally in combination with linear cross-section. Forexample, a chamfer may include a curved cross-section. The chamfer mayserve to compress the seal rings as the shaft with the seal ringsreceived in the radially opened slots is inserted into the bore.

Although during use or operation, the seal rings will typically wear-inunder gas loading, some abrasion of the walls forming the radiallyoutwardly opened slots is likely to happen as well. In various exemplarysealing assemblies the surface of the radially outwardly opened slots11, 12 and 13 are therefore optionally hardened to avoid abrasion of thewalls forming the radially outwardly opened slots. In various exemplarysealing assemblies a bush 15 is optionally fit on the shaft 10,replacing the section of the shaft that comprises the radially outwardlyopened slots 31, 32, 33. The bush avoids abrasion of the shaft 10 by theseal rings 31, 32 and 33. The bush 15 is optionally made of a materialthat is harder than the material of the shaft in order to avoid abrasionof the walls forming the radially outwardly opened slots.

To facilitate assembly/disassembly of the seal ring in the shaft, theseal rings are optionally divided by a split, as shown in FIG. 5 andFIG. 6. In order to minimise the size of the chamfer, the seal rings 30can have stop elements 35 and 36 on both sides of the split. The stopelements engage upon radial widening of the seal ring thereby limitingthe radial extension of the seal ring before the assembly, as shown inFIG. 5. When a seal ring is inserted in axial direction into the bore itgets radially compressed when led along the radially inward extendingchamfer, as shown in FIG. 6. As the stop element limits the radialextension of the seal ring, the size of each chamfer can be minimised.Also several seal rings with different outer diameters may be insertedin one mounting step into several seats with different inner diametersdue to the inventive chamfer located outward of each seat.

The sealing arrangement is drawn for the turbine side but the design canbe applied on the compressor side of the turbocharger.

It will be appreciated by those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. The presently disclosedembodiments are therefore considered in all respects to be illustrativeand not restricted. The scope of the invention is indicated by theappended claims rather than the foregoing description and all changesthat come within the meaning and range and equivalence thereof areintended to be embraced therein.

LIST OF REFERENCE SYMBOLS

-   10 Shaft, e.g. turbine wheel shaft-   11, 12, 13 radially outwardly opened ring slot-   15 Bush-   20 Housing-   21, 22, 23 Seat-   211, 221, 231, 233 Chamfer-   212, 222, 232 Step-   25 Bore-   26 Radially inwardly facing annular groove-   27 Drain channel    -   30, 31, 32, 33 Seal ring-   35, 36 Stop element-   A Axis, e.g. axis of rotation of turbine wheel-   p₂₁, p₂₂, p₂₃ Chamfer plateau radius-   r₂₁, r₂₂, r₂₃ Seat radius-   s₂₁, s₂₂, s₂₃ Step radius

1. A sealing assembly for sealing a shaft of a turbomachine in a bore ofa housing, said shaft extending from a hub of a turbine wheel to a shaftbearing in said housing, the assembly comprising at least two seal ringsand the bore comprising: a longitudinal axis extending generally from aninner end to an outer end of the bore, said outer end of the bore beingadjacent said hub of the turbine wheel; an outer seat disposed proximateto the outer end of the bore at an outer seat radius for an outer sealring, and an inner seat disposed axially between the outer seat and theinner end of the bore at an inner seat radius for an inner seal ring,wherein the bore comprises axially inward of an inner end of the outerseat and proximate to the inner seat a chamfer extending radiallyinwardly over an inward axial distance to an inner chamfer plateauradius.
 2. The assembly of claim 1, the bore further comprising axiallybetween the outer seat and the inner seat an intermediate seat at anintermediate seat radius for an intermediate seal ring and axiallyinward of the inner end of the outer seat and proximate to theintermediate seat a chamfer extending radially inwardly over an inwardaxial distance to an intermediate chamfer plateau radius.
 3. Theassembly of claim 1, wherein the inner seat radius exceeds the innerchamfer plateau radius and wherein the inner seat comprises a chamfer atthe outer end extending radially inwardly over an outward axial distanceto the inner chamfer plateau radius.
 4. The assembly of claim 1, furthercomprising a radial inwardly facing annular groove disposed axiallyoutward of the inner seat.
 5. The assembly of claim 4, wherein saidannular groove is connected to a drain channel.
 6. The assembly of claim1, the bore comprising: a plurality of seats disposed between said innerand said outer end of the bore at different seat radius for a pluralityof seal rings, wherein of each pair of adjacent seats the seat radius ofthe outward seat exceeds the seat radius of the inward seat,characterized in, that the bore comprises for each pair of adjacentseats axially inward of an inner end of the outward seat and proximateto the inward seat a chamfer extending radially inwardly over an inwardaxial distance.
 7. The assembly of claim 6, wherein the innermost seatcomprises a chamfer at the outer end extending radially inwardly over anoutward axial distance to an inner chamfer plateau radius.
 8. Theassembly of claim 6, wherein the bore comprises axially outward of anouter end of the outer seat a chamfer extending radially outward over anoutward axial distance from an outer chamfer plateau radius.
 9. A systemfor a turbomachine, the system comprising: a sealing assembly accordingto claim 1; a rotatable shaft, insertably positionable in the bore andcomprising at least two radially outwardly opened slots; and seal rings,positionable on the shaft, capable of being received by the slots andcapable of being seated in the seats of the bore.
 10. The system ofclaim 9, wherein at least one of the seal rings comprises a step gapwith a stop element.
 11. The system of claim 9, wherein the shaftcomprises a bush, and wherein said radially outwardly opened slots aredisposed in said bush.
 12. A turbocharger comprising: a compressor,comprising a compressor housing and a compressor wheel mounted in thecompressor housing; a turbine, comprising a turbine housing and aturbine wheel mounted in the turbine housing; a shaft connecting thecompressor wheel to the turbine wheel; a bearing housing disposedbetween the compressor and the turbine housings, the bearing housingdefining a bore that receives the shaft therethrough according to thesealing assembly of claim
 1. 13. The assembly of claim 5, the borecomprising: a plurality of seats disposed between said inner and saidouter end of the bore at different seat radius for a plurality of sealrings, wherein of each pair of adjacent seats the seat radius of theoutward seat exceeds the seat radius of the inward seat, characterizedin, that the bore comprises for each pair of adjacent seats axiallyinward of an inner end of the outward seat and proximate to the inwardseat a chamfer extending radially inwardly over an inward axialdistance.
 14. A system for a turbomachine, the system comprising: asealing assembly according to claim 8; a rotatable shaft, insertablypositionable in the bore and comprising at least two radially outwardlyopened slots; and seal rings, positionable on the shaft, capable ofbeing received by the slots and capable of being seated in the seats ofthe bore.
 15. A turbocharger comprising: a compressor, comprising acompressor housing and a compressor wheel mounted in the compressorhousing; a turbine, comprising a turbine housing and a turbine wheelmounted in the turbine housing; a shaft connecting the compressor wheelto the turbine wheel; a bearing housing disposed between the compressorand the turbine housings, the bearing housing defining a bore thatreceives the shaft therethrough according to the sealing assembly ofclaim 8.